This invention relates generally to exhaust hoods, and more particularly to kitchen exhaust hoods which do not have any built-in make-up air provisions.
It is possible to identify two major categories of kitchen exhaust hoods. Those in one category, hereinafter sometimes referred to as "exhaust-only" hoods, take air and fumes from over the cooking unit and exhaust it through the hood to the exterior of the building, thus removing heat and fumes from the area around the cooking unit. The hoods in the second category, hereinafter sometimes referred to as "make-up air" hoods, in addition to removing air from above the cooking equipment, introduce fresh air from outside the building to make up (at least partially) for that which is exhausted.
The disadvantage in use of exhaust-only hoods has been the fact that, due to relatively poor performance of some such hoods, it has been necessary to exhaust large volumes of air in order to be certain that all of the combustion products and fumes from the cooking unit are removed. The problem is that air must be taken from the kitchen to make up for the air that has been exhausted from the hood. At locations and during periods of the year when it is necessary to heat or cool room air for the comfort of the occupants, a significant amount of energy is used in either heating or cooling the room air and attempting to control the temperature thereof. So it is undesirable to have this "tempered" air removed from the building by the kitchen exhaust equipment.
To deal with this problem, hoods have been designed to provide their own make-up air. To do so, such hoods have air movers operating to bring air into the hood assembly from outdoors, in an amount comparable to that being exhausted. For example, in the hood disclosed in my U.S. Pat. No. 4,089,327 issued May 16, 1978, approximately 80% of the air that is exhausted is brought in by the make-up air mover in the hood. Higher percentages of make-up air can be used, if desired. In some such hoods, means have been used to introduce air from the hood into the room, other than directly to the area over the cooking surface. Examples are shown in the Sweet et al. U.S. Pat. No. 3,457,850 issued July 29, 1969, the Kaufman et al. U.S. Pat. No. 3,890,887 issued June 24, 1975, and the Jacobs U.S. Pat. No. 3,980,072 issued Sept. 14, 1976.
Make-up air hoods have shown significant advantages over the exhaust-only hoods, in terms of minimizing the impact of hood exhaust on the room environment, but there are some disadvantages to them. For example, because relatively large volumes of air are used, the blower sizes and power requirements are significant. In addition, the introduction of air requires a blower or blowers for that purpose, resulting in an installation that is or can be twice as expensive in terms of air moving equipment, as an exhaust-only hood. Also, it adds some complexity to the hood construction itself and the related ductwork and rooftop equipment. Therefore, there has remained a significant need for exhaust-only type hoods but with performance sufficiently high to permit the use of them with only a modest impact on the heating and cooling loads on the building environmental control equipment. The present invention meets this need.
My U.S. Pat. No. 4,200,087, issued Apr. 29, 1980, and U.S. Pat. No. 4,462,387, issued July 31, 1984, disclose inventions in the make-up air type of hood. The present invention is incorporated in an exhaust-only hood.